Except that it does - up to a certain point.
That's one of the few repeatable, tested, and validated economical principle from the XX century. Counter intuitive as it is, there's just no point denying it.
The only difference between theft and charity is your personal moral inflection.
I am an advocate for charity. But redistribution through taxation feels like stealing to me.
If there's a good reason to think that redistributing wealth will improve people's ability to mitigate risk and make good decisions, then your feeling would really be irrational and should be ignored.
I think that they aren't really socialist countries, I would point to places like Sweden and France as closer to actual socialism than North Korea, which is really a Fascist dictatorship explicitly modelled on pre-second world war Japan.
Vietnam is an odd one out here because having suffered a total catastrophe in the years running up to 1975 (as in the complete physical destruction of the state, mechanisms of production and the labour force via being killed in large numbers) the Vietnamese state has made huge progress to become relatively prosperous. There is a lot to be admired in terms of economic gain, although not much to be admired about freedom and safety for those with contrary views.
Redistribution increases the total wealth, and it is not a small effect at all.
But only up to a certain point. Complete communism still completely sucks.
It's been revised and remodeled several hundreds of times, if you want to search Google Schoolar or something like that, look for "demand side" theories, or crisis of "aggregated demand". Also, if you search for NGDP, the biggest share of the papers will be about this.
There are many other terms that will lead to less results. It's a really widespread concept.